I don't think it's so much of a fact of multiple guns on the table. It's more a matter of maturity and respect for the firearms and ammunition being fired. I have a shooting buddy that lives a few hours away and my wife and I visit him and his family from time to time. When we do get together, we compare the guns we have acquired since our last meeting and we like to shoot our usual favorites, too. So we sometimes have 4 or 5 pistols on the shooting table at the local indoor range. However we are very careful with each, only shoot one at a time, and are very conscious of where the ammo is going. The range doesn't seem to mind.
While shooting a number of guns at one time is inherently not a big deal, it's the loss of respect for the firearm, carelessness from confusion with so much going on, or not handling the weapons safely. Which there are already rules at most gun ranges for this kind of behavior.
Mike